Synchronizing

It means that the phase angle between the output waveforms is zero degrees.

PW's right about the phase angle, and the voltages must be the same also.

It means lots of excitement and expense if you get it wrong.

Generators and their drives can be ripped from their beds and with them the engineers that were also in their beds.

Getting synchronisation right is very important for ones personal comfort.

BAB.

To synchronise you must match voltage, frequency and phase angle at the same time. You normally have the machine that is coming on to the bus speeding up towards the correct phase angle so it will accept the load as breaker closes.

Peterd,

You are right! You need a master control with synchroscope, phase monitor etc.. This is usually used for paralleling two generators.

For synchronizing, phease sequence ,frequency and voltage of both the alternator should be same. Once the parameters matches ,then you can go for synchronising. There are different methods like all dark and all faint lamps etc.

I agreed your point i.e voltage, frequency and phase angles should match. if different capacities and aging ( one machine is 10 years old and one machine is new ) - what is the solution for syschronizing ?

Regds

A.Ravindra Reddy

Age of machine has nothing to do with it. Preferably the prime mover and/or the generator voltage regulator should have drooping characteristic for sysnchronising but not necessarily - depends on several things

Synchronizing two or more generators is to bring them in parallel operation in order to feed a certain electrical load. To be possible to put ac generators in parallel (to make them work together) as a prerequisite a) tension output of generators must have the same frequency (speed control by fuel or water injection at the generator's driver) b) output tension must match (excitation control at the generators) c) when phase angles between the equivalent phases of different generators are null, generators can be put in parallel by closing generator breakers.

These are the prerequisites for an ideal synchronization. The real world is somewhat different:

1 - Synchronize two generators without load (when the electrical load that must be feed exceeds the output of only one generator, so generators must be synchronized prior to close the breaker to feed the load)

2- Synchronize one generator with other generators that are just feeding a network.

In case 1, synchronization is made as described with two minor differences:

a) closing breaker order is given before phase angles are matching in order to compensate the closing time of the breaker;

b) output tension of both generators do not totally match, to be possible to have same reactive power maintaining generators electrically locked after synchronization.

In case 2 the new generator to be brought in parallel is synchronized

a) with a slightly higher frequency than the net (to take same load as soon as is breaker is closed;

b) with a tension slightly higher to feed same reactive power to the network

c) with a slight negative phase angle at the moment of breaker closing order.

These parameters (frequency, tension and phase angle) can be adjusted with an automatic synchronizing device and according with time response of the automatic speed/load control, the inertial momentum of the machine and time response of the automatic voltage regulator and breaker time to close. All these settings are more accurately established as the generators are more powerful and can impact all electrical system.

After synchronizing generators, how they will share the load that is another matter. Active and reactive power share can be manually controlled via fuel or water injection at the generator driver (diesel, gas or hydro turbine) and excitation at the generator excitation coils respectively, but usually all share activity, is automatically controlled by an automatic speed/load control device that controls the generator driver and the automatic voltage regulator device (excitation control) and their characteristic response curves. Settings of these devices must be more accurately established when generators with different prime movers like diesel and hydro with quite different time responses to changing load.

So type of prime mover, total rotating mass and age of prime mover related with time response to sudden variation of load can be important on choosing the right settings of automatic control devices in order to maintain generators synchronized but are of almost no importance to synchronize them.